高强Ti-IF钢铁素体区热轧和冷轧过程织构演变规律

为了揭示铁素体区热轧、冷轧和退火过程中高强Ti-IF钢中织构的演变过程,采用X射线衍射仪研究了铁素体区热轧及随后的冷轧和退火织构的特点.研究表明,在铁素体区热轧后,表面和中心面的织构类型和强度不尽相同,表面上的主要织构组分是剪切织构{110}<001>,而中心面上的主要织构组分是{001}<110>～{223}<110>和{111}<110>,由于织构的遗传性,冷轧和退火后的织构在表面和中心面上也不相同;经不同压下率冷轧后,织构变化趋势一致,表面上{110}<001>组分消失,{001}<110>成为最强组分,而中心面上最强组分由{001}<110>沿α取向线向{112}<110>偏移,冷轧织构由α织构和γ织构组成;退火后,表面上织构的变化与以往结论有所不同,{001}<110>～{112}<110>组分减弱,而γ取向线上的{111}<123>组分增强,{111}<112>和{111}<110>减弱.     

IF钢铁素体区热轧和退火过程中织构的演变

研究了一种Ti—IF（Interstitial—free）钢在铁素体区热轧和退火过程中织构的变化．由于轧制过程摩擦的影响,热轧织构和退火织构在厚度方向上都有很大的差异．在钢板的表层,热轧织构的主要组分是{110}（001）,退火后表层的铁素体晶粒没有发生再结晶,该组分转变为（001）（110）;在试样的中心和1／4面,热轧织构组分主要是较弱的（111）／／ND（板法向）织构和部分（110）／／RD且在{001}（110）处最强;退火后中心面上的晶粒发生了完全再结晶,{001}组分转变为（111）／／ND组分使（111）／／ND织构成为唯一织构组分且在{111}（112）处最强．     

Finite element analysis and experimental study of microstructure evolution of nitrogen alloyed ultralow carbon stainless steel during hot deformation

Abstract

Hot compression experiments of a nitrogen alloyed ultralow carbon stainless steel were performed in the temperature range of 1223–1423 K, at strain rates of 0.001–1 s^?1, and with deformation amounts of 30–70% on a Gleeble-3500 thermal-simulator. Based on the results from thermo-physical simulation experiments and metallographic analyses, a physically-based constitutive model and a dynamic recrystallisation (DRX) model of the studied steel were derived, and the developed models were further embedded into a finite element method (FEM) software. The microstructure evolution of the studied steel under various hot deformation conditions was simulated by FEM, and the effects of deformation amount, strain rate and temperature on the microstructure evolution were clarified. The results obtained from the finite element analysis were verified by the experiments. The finding confirms that the thermal-mechanical FEM coupled with the developed constitutive model and DRX model can be used to accurately predict the microstructure evolution of the studied steel during hot deformation.     

Microstructure evolution in heat affected zone of T4003 ferritic stainless steel

In this work, microstructural characteristics and development within the heat affected zone (HAZ) of T4003 ferritic stainless steel (FSS) welded joint were investigated combining experimental measurement with finite element simulation of welding temperature field. The results indicate that the HAZ was characterized with heterogeneous microstructure due to the extensive peak temperature range which could be divided into three sub-zones named as HAZ1, HAZ2 and HAZ3. The HAZ1 (the region next to weld zone boundary) experienced peak temperatures of 1300–1500 °C during welding process. This region presented almost fully δ ferrite microstructure with irregular grain, which was attributed to the high element diffusion rate and the absence of elevated-temperature austenite. The HAZ2 (center region of HAZ) suffered the peak temperatures of 1150–1300 °C. It presented martensite + δ ferrite dual microstructure with limited grain growth due to the formation of γ phase at grain boundaries. The HAZ3 (the region closed to the base metal) was undergone the peak temperatures of 830–1150 °C and was characterized with both martensite and ferrite structure.     

Effect of boron on hot ductility oflow carbon low alloyed steel

Abstract

The influence of boron on the hot ductility of C-Mn-Al-Cr steel has been investigated. At <980°C M(CB)₃ precipitated out and about half of the boron content was in solution in austenite at >900°C. It was found that solute boron atoms segregate to austenite grain boundaries and occupy the vacancies induced by deformation. This prevents the formation and propagation of microcracks at boundaries and results in improved hot ductility and a reduced dynamic recrystallisation temperature.     

Constitutive modeling of ferritic stainless steel

In this work, constitutive models, including phenomenological and crystal plasticity, were used to simulate the anisotropy behavior and texture evolution of two ferritic stainless steel sheets, AISI409L and AISI430. Uniaxial tension, hydraulic bulge and disk compression tests were performed to characterize the mechanical properties of the two materials, and to determine the yield surfaces at different amounts of plastic work. Meanwhile, X-ray diffraction and electron backscatter diffraction techniques were used to analyze the texture of undeformed and deformed specimens. Crystal plasticity simulations were performed to determine the plastic behavior in selected deformation paths. The analysis of the mechanical test results showed that the yield surface shapes were changing during deformation. Crystal plasticity results indicated that texture evolution was mainly responsible for the yield surface shape change, i.e., anisotropic work-hardening, in AISI409L. For AISI430, the results were not completely consistent. More work is needed to understand the plastic behavior of this material.     

Texture evolution in stainless steel processed by selective laser melting and annealing

This work analyses the texture and microstructure gradients emerging in a 316L stainless steel processed by selective laser melting, using an island scan strategy, followed by annealing. Laser processing leads to the alignment of different crystallographic directions with the build direction at the mid and top layers, as well as to gradual structural coarsening. Annealing triggers discontinuous recrystallisation at highly strained regions, such as grain boundaries and laser track centre lines, resulting in the onset of new texture gradients. The development of the mentioned texture gradients is rationalised based on a competition between thermal gradient-driven growth and epitaxial growth.     

Modelling surface ridging in ferritic stainless steel

Abstract

A new model is proposed to account for the occurrence of surface ridging (parallel corrugations) in ferritic stainless steel. In the absence of notable texture component clustering, it is shown that local anisotropy in plastic behaviour can still occur on a scale considerably larger than the grain size. The construction of a simple finite element model incorporating plasticity data from microtexture measurements demonstrates that parallel surface corrugations can be simulated during uniaxial tensile straining. It is shown that the corrugation profile is the result of the superimposition of a number of differential transverse strains that contribute to the overall deformation induced bending.     

热轧后退火对超纯铁素体不锈钢表面皱折的影响机理

以一种铌、钛双稳定化超纯Cr17铁素体不锈钢的热轧板和热轧退火板为初始材料,分别经相同的冷轧及退火处理,从显微组织演变、微织构演变的角度研究了热轧后退火对成品板表面皱折的影响机理.研究结果表明,与热轧后不退火相比,热轧后退火可使冷轧退火板的最大皱折高度和平均皱折高度分别降低37.0%、35.6%.热轧后退火有利于热轧板...     

不锈钢/高硼不锈钢层状复合材料组织变化

为了解决高硼不锈钢材料变形难度大、易开裂、塑性低等问题,采用复合浇铸-热轧变形工艺,制备了以难变形金属高硼不锈钢为中间层的层状复合板,研究了复合材料在铸造、热轧和固溶处理各阶段的组织特点及芯层中硼化物的相组成规律.结果表明:含硼质量分数2%～2.5%的复合板芯层的铸态组织主要以共晶组织形式凝固,含硼较高的芯层铸态组织除以共晶组织形式凝固外,还形成大块的含有Cr2B和Fe2B的过共晶硼化物相;热变形使共晶硼化物发生破碎、细化,但过共晶硼化物的体积形状变化不大;固溶处理使覆层中细小的二次析出物明显减少,这有利于复合板的力学性能,但芯层中硼化物的形貌、数量及尺寸变化不大.     

Analysis of ridging in three ferritic stainless steel sheets

Abstract

In the present work, three types of ferritic stainless steel sheets AISI 430A (16%Cr), AISI 430E (16%Cr, 0·36%Nb) and AISI 434 (16%Cr, 1%Mo), known to display different ridging behaviours, were characterised in both microstructure and texture using optical metallography and electron backscatter diffraction techniques. It was concluded that surface microridging is a result of the differential plastic behaviour of {111}〈uvw〉 and {001}〈uvw〉 grain colonies existing in the sheet; severe ridging (undulations) is a consequence of through thickness texture and microstructure inhomogeneities that lead to grain buckling under internal compressive stresses.     

Failure analysis of ferritic stainless steel locking ring

A locking ring made of Ferritic stainless steel, fitted in a pressure gauge, failed after the service of seven years. The mode of failure was analyzed by using Scanning Electron Microscope and optical microscope. A finite element model proposed in this work demonstrated the stress distribution in different regions of the locking ring. It was observed that the ring failed in the same region where the maximum stresses were predicted. Furthermore, a detailed study on the mode of failure found that the failure occurred in stress corrosion cracking conditions.     

Intermediate-temperature brittleness of a ferritic 17Cr stainless steel

A ferritic 17Cr stainless steel was tensilely tested at high temperatures and an intermediatetemperature brittleness, which showed a low reduction of area, was observed. The brittleness occurred near 810 to 970 K. The intermediate-temperature brittleness shifted to higher temperatures at higher tensile strain rates.     

Microstructural analysis of friction stir welded ferritic stainless steel

High-quality, defect-free welds were successfully produced in 409 ferritic stainless steel by friction stir welding. A remarkably fine-grained microstructure was observed in the stir zone, and the fraction of low angle grain boundary in the stir zone significantly increased as compared to that in the base material. An increase in plunging depth led to an increase of the fraction of low angle grain boundary, a decrease in grain size, and an increase in hardness in the stir zone.     

Hydrogen cracking of ferritic stainless steel thermal storage tanks

A ferritic stainless steel (SUS436L), which was subjected to various kinds of reduction ratio was precharged with hydrogen at 40°C in 15% HCl solution by employing galvanic reaction with zinc. Tensile tests were performed in air at room temperature on both uncharged and charge specimens. Finite element method (FEM) analyses were carried out to obtain strain at panel corners under various different internal radii in a thermal storage tank when it was subjected to internal pressure. As a result, it was found that the value of internal corner radius?thickness of the panel (R?t) should be more than about 2 in order to prevent hydrogen embrittlement cracking.     

一种新型铁素体不锈钢的深冲性能研究

为探究一种新型铁素体不锈钢的深冲性能,在840~920℃不同温度下对新型铁素体不锈钢的冷轧板做再结晶退火处理,通过XRD、SEM和EBSD等分析方法研究了退火2 min或4 min后,材料微观组织、宏观织构的变化规律对深冲性能的影响及其内在机理.研究表明:保持退火时间2 min,退火温度900℃时,试验钢拥有较多的有利γ纤维织构,主要为{111}112取向,并有少量α纤维织构,此时平均塑性应变比r-=1.77,高于其他退火温度下的值;延长退火时间,在900℃下保温4 min,不同取向晶粒获得了长大机会,晶粒尺寸均匀性显著改善,r-值提高至1.82,试验钢有望取得理想深冲性能.     

Correlation between ductile-to-brittle transition behaviour and twinning in ferritic stainless steel

In this work, the 18Cr–2Mo ferritic stainless steel was treated with and without warm rolling at 573 K with 66.5% reduction after conventional hot rolling process. It was shown that ductile-to-brittle transition behaviour could be closely related to deformation twinning and parameters affecting critical temperature for twinning would also inevitably affect ductile-to-brittle transition temperature. This correlation between ductile-to-brittle transition behaviour and twinning was in good agreement with the Cottrell–Petch model. A lowered transition temperature and an improved toughness after introducing warm rolling process and corresponding annealing process could be mainly explained in terms of refining the recrystallised grains and reducing the volume fraction of grains having orientations favourable for twinning, which decrease the critical temperature at which twins form.     

Recrystallization of molybdenum- and nitrogen- alloyed austenitic stainless steels after hot working

Abstract

Hot compression experiments have been performed to study the influence of molybdenum and nitrogen on the kinetics of static recrystallization in four austenitic stainless steels: AISI 316L (17Cr–13Ni–2·5Mo), AISI 316LN (17Cr–13Ni–2·5Mo–0·17N), DIN Wnr.l·4439(18Cr–12Ni–4·4Mo–0·2N), and UHB 904L(20Cr–25Ni–4·5Mo–1·5Cu). Experiments were carried out both for wrought and cast materials at temperatures of 1050–1250°C and to strains between ε = 0·10 and ε = 0·40. It was found that the static recrystallization was delayed by a factor of about 1·7 in time when raising the molybdenum content from 2·5 to 4·5 wt-%. Nitrogen was found to have no significant effect on the rate of static recrystallization. Cast material recrystallized more slowly than wrought material and this could not be attributed only to a grain size effect. Increasing strain and temperature resulted in a reduced recrystallization time. The recrystallized grain size decreased with increasing strain and decreasing temperature. Empirical expressions could reproduce with excellent accuracy the strain and temperature dependence of both the fraction recrystallized and the recrystallized grain size.

MST/360